U.S. Pat. No. 4,193,691 refers to a spectrometer which comprises a slit assembly manufactured in file form of a liquid crystal cell. The electrodes of the cell can be selectively actuated for producing a pattern of so-called "slits" (temporarily transparent portions of the cell) which are arranged in a specific manner. Such a liquid crystal cell with a selectively actuatable pattern of "slits" capable of switching between clear and opaque optical states has acquired the name optical shutter. The spectrometer described in U.S. Pat. No. 4,193,691 comprises means for producing a spectrum of light under analysis, means for directing that spectrum on to the above-described slit assembly (where the slits have configurations appropriate to positions of specific spectral lines of interest in the spectrum), and also comprises detection means for detecting a portion of the spectrum which has passed the slit assembly at a specified time. The detected signal is then transmitted to so-called utilization means, i.e. the means by which the detected signal may be processed.
It should be emphasized that the concept of the above-described device resides in obtaining the spectrum of the light under analysis prior to directing radiation to the slit assembly. In accordance with this concept, the description specifically refers to a prism as the classic means for producing the spectrum. The conventional character of these means is further testified by the fact, that in all embodiments described in the specification the spectrum producing means are positioned before the slit assembly. However, such a configuration where the spectrum producing means precede the optical shutter cannot be considered as being the one the most compact and easy to manufacture.
U.S. Pat. No. 5,457,530 describes a "Spectrometer provided with an optical shutter" which follows the above-mentioned concept of first obtaining a light radiation spectrum and further directing it to an optical shutter array for selectively transmitting therethrough predetermined spectral lines (i.e. wavelength-dependent bands) at specified time intervals for further detecting and processing the intensity of these lines. The main involvement of the spectrometer of U.S. Pat. No. 5,457,530 in comparison with that of U.S. Pat. No. 4,193,691 is that, in the former, the optical shutter array includes a plurality of optical shutter elements arranged in correspondence with the lines in the obtained spectrum and being made of a material (PLZT) characterized by the increased switching speed of the optical state. Another difference is that the spectrum producing means constitutes a diffractor by which an incident light beam is diffracted according to wavelengths.
It is quite natural that methods of spectral analysis realizable by the known spectrometers which comprise optical shutters, are all based on the same approach in that the initial band of optical radiation must first be decomposed into a spectrum comprising a predetermined number of optical portions, each including predetermined wavelengths, which optical portions are then processed for further calculations. The optical shutter in the described methods (and devices) is used for high-speed switching between the mentioned optical portions of the spectrum. Such methods impose high requirements on the accuracy of the described optical equipment which is therefore expensive.
U.S. Pat. No. 5,424,545 describes a method for non-invasive non-spectrophotometric infrared measuement of blood analyte concentrations. The method includes either illuminating a sample with a plurality of radiation beams each covering a distinct portion of the spectrum and partially overlapping one another, or detecting radiation reflected or transmitted by the sample using a plurality of broadband detectors having at least partially overlapping responses. The obtained signals are coded and analyzed by analogy to colorimetry and visual processing and can be converted into concentration measurements. The computational method is based on implementation of the idea of color perception for a quantitative substrate analysis, which renders the method complex and time consuming.